A new nightmare is threatening British farmers, already reeling from BSE-infected cattle, the fall in lamb prices and swine fever. An emergency ban on the export of meat and live animals was introduced last night following the first outbreak of foot and mouth disease for 20 years.

A five-mile exclusion zone has been set up round an Essex abattoir, where vets have found 27 pigs infected with the disease, and a neighbouring farm, where cattle have been found to be infected.

Two other farms - on the Isle of Wight and in Buckinghamshire - which supplied the abattoir with pigs, plus a fourth farm in Gloucestershire, are also in quarantine. Dozens more are being examined.

The moves may seem draconian, but there are few more virulent viruses than foot and mouth. The last major epidemic, in 1967, spread rapidly across Shropshire, Cheshire and Wales, infecting 2,346 farms in an eight-month period and requiring 433,000 animals to be slaughtered before it was eliminated.

Infection can spread via vehicle tyres, human feet, contact with diseased animals or even through the air. Rats and even starlings were thought to have been involved in spreading the 1967 epidemic. Hence the five mile exclusion zones. The wife of the Isle of Wight farmer whose pigs are suspect was stranded outside her farm yesterday and staying with neighbours. It could take up to 10 days to clarify whether the farm was a source of the infection.

The new food standards agency rightly moved quickly to reassure the public yesterday that the disease posed no serious threat to the human food chain. The disease is confined to animals with cloven hooves. Nor can intensive factory farming methods be blamed for this outbreak.

The disease dates back at least 150 years, long before farmers began speeding up growth by turning natural herbivores, such as cows, into meat eating animals by feeding them minced up meat ends and chicken litter - a procedure now banned following the BSE scandal. Undoubtedly the hygiene of the food chain, from farm through processors, distributors and retailers, could still be improved, but foot and mouth cannot be blamed on a dirty food chain.

There was a small infection in 1981, which was quickly snuffed out with a rigorous quarantine regime and the slaughter of animals on suspect farms. Ministers ought to re-examine the alternative approach, used by some European states, of vaccinating animals against the disease.

Meanwhile, the National Farmers Union fully supported the government's moves: "While these measures will be devastating to the farms involved, it is in the interests of the whole UK livestock industry that this disease is stopped dead in its track."

Maintaining this cooperation is crucial. The most effective way will be to ensure that, unlike their treatment in 1967, compensation for affected farmers is fair and comprehensive.